Electron ray tube indicator circuit



Nov. 8, 1938. D. E. FOSTER ET AL ELECTRON RAYl TUBE INDICATOR CIRCUIT Filed April 21, 1957 Patented Nov. 8, 1938 UNirEo sA'r a ATENT ELECTRON RAY TUBE INDICATOR CIRCUIT Application April 21, 1937, Serial No. 138,108

7 Claims. (Cl. Z50-20) potential of the control element varies.

Our present invention relates to electron ray tube indicators, and more particularly to uniformly sensitive shade angle indicators of the electron ray tube type.

There has been disclosed and lclaimed in U. S. P. 2,051,189 issued on August 18, 1936, to l-I. M. Wagner, a variable shadow angle indicator of the electron ray tube type. Such an indicator tube generally comprises a direct .current amplier section, a fluorescent target, and an electron ray control element for the target which is responsive to the amplifier space current flow. The control element produces a shadow on the glowing target which varies in width as the negative When the control grid of the amplifier section .exerts uniform control effect on the amplier space current, the tube is of the type commercially designated as 6E5. The latter type tube uses a sharp cut-off triode for its direct current amplier; the shadow angle closes on a comparatively small value of negative potential on the amplier control grid. If, on the other hand, the amplifier section employs a control grid having a variable mu characteristic (a remote cut-oil amplier), then the shadow angle closes on a larger value of negative potential on the control element; such a tube is of the 6G5 type.

When utilized as a resonance, or tuning, indicator in a receiver employing automatic volume control (AVC) in the manner disclosed in the aforesaid Wagner patent actual experience has demonstrated that both the 6E5 and 6G5 types of indicator tubes have operating disadvantages. While the 6E5 type tube gives suitable indication for signals of low intensity (such as weak or distant signals), it tends to close the shadowy angle too quickly on stronger signals. This leads to confusion of the set operator when receiving stations of moderate and high intensity. 'I'he 6G5, on the contrary, gives satisfactory shadow response on strong signals, but is relatively insensitive for weak signals. To satisfy the requirements of all types of receiver operators, it is necessary that the indicator tube be of substantially uniform sensitivity for weak and strong signals.

It may be now stated that it is one of the main objects of our present invention to provide an electron ray indicator tube circuit Whose shadow angle varies appreciably at Weak or strong signal reception; and whose essential characteristie resides in the concurrent variation of the target potential with changes in the shadow width control element potential.

Another important object of our invention may be stated to reside in the provision of an electron ray tube circuit provided With a variable shadow angle; the target potential of the indicator being highly positive when the input voltage is relatively high, Whereas the target potential is materially decreased when the input voltage is small, and the shadow angle of the indicator tube thereby responding with substantial sensitivity at diiferent intensities of electric currents whose magnitudes are to be visually in-dicated.

Still other objects of this invention are to improve generally the eiciency and sensitivity of electron ray indicator tube circuits, and more especially to `provide visual indicator circuits capable of economical embodiment in radio receivers.

The novel features which We believe to be characteristic of our invention are set forth in particularity in the appended claims; the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which we have indicated diagrammatically a circuit organization whereby our invention may be carried into effect.

Referring now to the accompanying drawing, there is shown the circuit diagram of a radio receiver; the latter may be of the tuned radio frequency amplifier type, or it may be a superheterodyne receiver. In either case the detector, or audio demodulator, comprises a diode I having a tuned input circuit 2; the diode anode being connected to the high potential side` of' circuit 2, while the grounded cathode is connected to the low potential side of the latter through a load resistor 3 bypassed by condenser 4 for signal carrier frequency current. The condenser 5 -tunes the input circuit 2 to a desired carrier frequency, and the condenser may be xed or variable. The audio voltage component of detected signals is transmitted through condenser G to the audio utilization network, and the audio network may comprise one or more amplifiers followed by a reproducer.

The direct current voltage component of the potential developed across load resistor 3 is employed as AVC bias to control the signal amplifiers in gain so that the signal carrier amplitude at the demodulator input circuit 2 is substantially uniform despite wide signal amplitude variation at the signal collector I. The AVC bias is transmitted by lead 'l to the signal grids of the controlled amplifiers` The usual filter resistors S are used in the AVC lead for the suppression of pulsating voltage components.

If the receiver is of the T. R. F. type, the ampliers 9 and Il? are each provided with tunable input circuits Il and i2 respectively; the variable condensers iI and I2' of the latter have the rotors thereof uni-controlled with the rotor ci' variable condenser 5 so that the circuits ii, i2 and 2 are each tuned to the same carrier frequency. The input circuit II is coupled to the signal collector I, as at M; the circuit I2 is coupled, as at M1, to the output circuit ofv tube Q; the output circuit of amplifier I0 is coupled, as at M2, to the detector input circuit 2. Ii the receiver is of the superheterodyne type, then the signal amplier 9 would be followed by a converter, or first detector, tube whose I. F. output energy is amplied by one or Vmore I. F. amplifiers; the diode I acting as the second detector of the amplified I. F. energy. Of course, the AVC bias can be produced by a diode rectifier independently of the detector. In a superheterodyne receiver the AVC bias may be applied to the radio frequency and I. F. ampliers, as well as to the signal grid of the converter tube. While .the receiver may be of the broadcast type, it can,

also, be constructed to operate in a plurality of signal ranges which may include short wave signals.

`The electron ray indicator tube T is schematically represented; it will be understood that its construction is clearly disclosed in the aforesaid Wagner patent. Those skilled in the art are fully aware of the mode of constructing and operating a tube of this type hence, the schematic representation will be understood to depict a 6E5 tube. Since correct tuning of a receiver by ear is made diicult by the AVC action for "well known reasons, the BEE type tubeprovides a convenient and simple device for visually indicating the point of exact reasonance of a receiver at the different settings of the tuning mechanism. To review, in a general way, the construction of the Vindi'- cator tube, the latter includes a triode mounted in a glass bulb; the triode is indicated by the cathode section I3, the control grid I 4 and plate I5. A fluorescent target I6 is mounted in the dome of the bulb, and has the shape of a conical irustrum. The observer views the interior face 'of the target which is coated with a fluorescent material. The target is connected, by lead I'I' and resistor R, to the +B terminal of the voltage supply source for the amplier 9.

The positive plate of amplifier 9 is connected to the +B terminal through resistor R, the cathode of the amplifier being grounded through the grid bias network 9. 'Ihe positive target I6 attracts electrons from the second cathode section Iii. These electrons cause the fluorescent coating of the target to glow, and the target has, therefore, the appearance of a ring of light. Both cathode sections i3 and I8 are established at ground potential.

The numeral I9 denotes an electrode, the electron ray control electrode, which is mounted between the cathode section I8 and the target I6. When the potential of electrode I9 is less positive than the target, electrons owing to the target are repelled by the electrostatic eld of the electrode, and, hence, the electrons do not reach that portion of the target directly behind the electrode I9. Because the target does not glow in the area where it is shielded from electrons, the control electrode I9 produces, or casts, a shadow on the glowing target. The extent of this shadow varies from approximately degrees of the target, when the control electrode I9 is much more negative than the target, to Zero degrees when the control electrode is at approximately the same potential as the target. The potential of the electrode IS is determined by the direct current voltage on the control grid-I4. The flow of the triode space current through resistor R1 produces a voltage drop which determines the direct current potential of electrode I9.

The control grid ifi is connected to ground through a leak resistor 2U, the bypass condenser 2l beingconnected between the grounded lead of the cathode sections of tube T and the control grid I4. The electrode I9 is connected to the plate I5 within the tube envelope, and the plate I5 is connected to the plate side of resistor R through a path which includes the load resistor R1 and the lead Il; it will be noted that the target I6 is connected to the junction of lead I'I and resistor R1. A bypass condenser 22 is connected to ground from the lead I'I. It will be seen that the direct current voltage which is impressed on the control grid lli is AVC bias. Accordingly,`when no signals are received there will be no direct current voltage impressed on control grid lli, because in the no-signal state AVC voltage is not produced.

When the voltage on the grid Il! changes, in the positive direction, the current ow through resistor R1 increases; with the result that the control electrode i9 becomes increasingly negative in potential, and, therefore, the shadow angle on the target I6 widens. Conversely, as the AVC bias applied to control Vgrid iti increases, then the current flow throughresistor R1 decreases; and the shadow angle on target I6 narrows because of the decreasing negative potential on electrode I9.

The tube T will then function as a tuner indicator for the radio receiver. Since the AVC bias is at a maximum when the set isv tuned to give maximum response at a Ydesired station setting of the tuning means, the shadow angle on target I6 is at a minimum when the set is tuned exactly to the desired station. Thus, the electron ray tube givesV a convenient visual indication of correct tuning. The 6E5 tube employs a sharp cuto triode which closes the shadow angle on target I on a comparatively small value of AVC voltage. The 6G5 type of tube has a remote cut-off trio-de which-closes the shadow angle at a larger value of AVC voltage than the 6E5 tube.. As explained before, however, the 6E5 tube is not sensitive for signals of moderate, or relatively high, intensity. Conversely, the 6G5 tube is sensitive for strong signals, but has poor sensitively on weak signals.

In the circuit arrangement for the indicator tube T, as shown in the drawing, it is possible to secure relatively large changes in shadow angle for weak signals without too rapid closing of the shadow angle on strong signals. When the AVC bias is large, the potential drop e across resistor R will be small, and-the voltage E will approximate the potential at'the -l-B terminal of the voltage source. For small, or zero, AVC bias the voltage E-will be equal-to the --B voltage minus the voltage drop e. @In such case the voltage e will be large because the space current through the triode of tube 'I is large when the AVC bias is a minimum. These voltages and circuit constants may be proportioned to secure a'value for E whichv isnear 250 volts for strong signals, thus limiting the shadow angle'width of the indicator tube for strong signals. In the no-signal state the voltage E may be small, near 100 volts, thus increasing the sensitivity of the indicator tube for weak signals,

In other Words, the operating potential E of the target I6 is varied concurrently with the magnitude of the AVC bias applied to the triode control grid I4. When the target I6 is at a small positive voltage, deection of the electrons flowing from the cathode section I8 to the target I6 is readily accomplished. When the target potential E is increased it requires a relatively larger negative voltage on the electrode I9 to produce a corresponding deiiection of'the electrons from target I6. In other Words, the glow section of tube T is made stiffer in electron deflection characteristic when the potential of the target I6 is increased in `a positive sense. Plate I 5 differs in potential from target I6 by the drop across resistor R1. They will vary in the same direction in potential With changes in drop across R, but not in the same proportion because of R1. It must be remembered that changes in target and plate potentials are due to the AVC bias Which is applied to the electron ray tube grid as Well as to tube 9. The target current is substantially independent of grid or plate potential, but the current to plate l5 varies therewith so that the change in plate current with bias actually aids the eiect sought.

The +B voltage is appreciably higher than 250 volts. For example, with +B equal to 400 volts, and resistor R having a value of approximately 30,000 ohms, the Voltage e at zero bias on amplifier 9 will be 300 volts. It is assumed that the amplifier 9 is a pentode of the 6K7 type, and the current of this type of tube is 4-5 milliamps.; that of the electron ray tube T is approximately 4-5 milliamps. The plate current ow of the tube T is not appreciably aected by the AVC bias applied to grid I4, whereas the plate current of the amplifier 9 at -20 volts (AVC bias) is approximately 0.8 milliamps. Thus, with no AVC bias produced the operating voltage E of the target I6 of tube T will be 100 volts, and With an AVC bias of -20 volts, E will' be equal to 250 volts. It is also pointed out by way of illustration that resistor R1 may have a value of 0.5 to 1.0 megohms.

It is to be clearly understood that the present .invention is not limited to the utilization of the radio frequency amplifier 9 as the tube Whose plate circuit resistor is employed for developing the voltage e. As a matter of fact, any other type of tube may be used for this purpose; in fact, a special tube may be used which is independent of the signal transmission function of the receiver. It is preferred to employ a radio frequency amplifier to develop the voltage e, because the resultant changes in plate impedance of amplifier 9 with AVC bias has little effect on the receiver performance. It will now be seen that by means of the present invention the indicator tube is made highly sensitive for Weak, or distant, signal reception by virtue of the fact that the AVC bias, which is a minimum for such reception, acts in such a manner that the positive potential of the target of the indicator tube is relatively low thereby permitting ready deflection of the electrons owing to the target. On the other hand, when the signals are strong, or when the receiver is tuned exactly to resonance in the case of strong signal reception, the AVC- bias is a maximum, and this results in an increase of the target positive potential to a value such that it is relatively more difficult to deflect electrons owing to the target. Accordingly, for strong signal reception it takes relatively larger AVC bias to close the shadow angle of the indicator tube.

While we have indicated and described a system for carrying our invention into effect, it will be apparent to one skilled in the art that our invention is by no means limited to the particular organization shown and described, but that many modications may be made Without departing from the scope of our invention, as set forth in the appended claims.

What is claimed is:

1.' A method of visually indicating the magnitude of direct current voltages which includes the steps of projecting electrons upon a fluorescent target, applying a positive potential to said target, deilecting electrons from said fluorescent target in response to changes in magnitude of a direct current voltage, and varying the positive potential of said target over a relatively Wide potential range concurrently with changes in magnitude of said direct current voltage.

2. A method of operating a visual voltage amplitude indicator tube of the type which includes at least a cathode, a uorescent target adapted to receive electrons from said cathode, and an electron control electrode disposed between the target and said cathode, said method including the steps of varying the direct current potential of the control electrode in response to a change in magnitude of a direct current voltage Whose amplitude is to be visually indicated, and concurrently varying the positive potential of said target over a relatively Wide potential range with respect to the cathode as said direct current voltage amplitude changes.

3. A method of visually indicating resonance conditions in a radio receiver of the type employing an AVC circuit and an indicator tubeV which is provided with at least a cathode, a flucrescent target and an electron control electrode arranged to deflect electrons from said target, the method including the steps of varying the control electrode potential in response to changes in automatic volume control potential, and simultaneously changing the positive potential of said target over a relatively Wide potential range in response to said changes in volume control potential.

4. In a voltage visual indicator circuit, an electron ray tube of the type including a cathode, a fluorescent target, and an electron control electrode disposed within said tube to deflect electrons from said target, means to establish the target at a positive potential with respect to the cathode, means for varying the direct current potential of said control electrode in response to changes in amplitude of direct current voltage which is to be indicated, and additional means for varying the positive potential of said target over a relatively Wide potential range in response tolsaid voltage amplitude change.

5. In combination With -a radio receiver of the type employing an automatic volume control circuit, a tuning indicator tube which comprises an amplifier section and an electrode section, said last section including at least a cathode, an electron control electrode and a iiuorescent target, said control electrode being at the same direct current potential as the output electrode of said amplifier section, means for applying volume control po-tential to the control grid of the amplifier section, means including a load, element for ap- ,direct current potential drop across said load element over a relatively Wide potentialrange in response torcnanges in volume control potential.

6. In combination with a radio receiver of the type employing an automatic volume control circuit, a tuning indicator tube which comprises an amplifier section and an electrode section provided With at least acathode, an electron control electrode and a fluorescent target, said control electrode being at the same direct current potential as the output electrode of said amplifier section, means for applying volume control potential to the control grid of the amplifier section, means including a load element for applying a positive potential to said target, means responsive to space current Vilovv of said amplifier section for varying the potential of said control electrode, additional means for varying the direct current potential drop across said load element in response to changes in volume control potential,

said receiver including a signal amplier having its signal grid connected to said volume control circuit for gain control of the amplier, and said load element being disposed in the space current path of sai-d amplifier.

'7. In combination with a radio receiver of the type employing an automatic volume control circuit, a tuning indicator tube which comprises an amplifier section and an electrode section Which includes a cathode, an electron control electrode and aY iluorescent target, said control electrode being attheV same direct current potential as the output electrode of said amplier section, means for applying volume control potential to the control grid of the amplifier section, means including `a load element for applying a positive potential to said target, means responsive to space'current flow of said amplier section for varyingthe potential of said control electrode, additional means for varying the direct current potential drop across Said load element over a relatively Wide potential range'in response to changes in volurneicontrol potential, and said control electrode being disposed in the indicator tube so as to deflectelectrons frorn` said target whereby a shadow of variable Width is produced on the target, and the positive potential of said target being a maximum Wljien said Volume con trol potential is a maximum.

l DUDLEY E. FOSTER.

GARRARD MONTJOY. 

